Autoimmune and Paraneoplastic Disorders.

Autoimmune encephalitis (AE) is a disorder in which the immune system targets the central nervous system. AE can be paraneoplastic or postinfectious, though many cases lack a clear trigger. AE typically presents acutely or subacutely with altered mental status and psychiatric symptoms, with clinical features varying by the targeted autoantigen. MR imaging is the imaging modality of choice and may show T2 and fluid attenuation inversion recovery (FLAIR) hyperintensities in the medial temporal lobes, characteristic of limbic encephalitis, though imaging can be normal or may extend beyond the limbic system. Key differentials include infectious encephalitis and tumors.